Practice question

Inner membrane metabolite carriers including ADP/ATP antiporter ANT1-3, phosphate carrier PiC, dicarboxylate, citrate, aspartate-glutamate belong SLC25 family tripartite three repeats each two helices total six without cleavable presequence. Internal targeting hydrophobic modules recognized post-translationally. After synthesis cytosol association Hsp70 Hsp90 chaperones cross outer TOM complex using Tom70 receptor. Intermembrane space TIM chaperone hexameric small Tim proteins Tim9-Tim10-Tim12 twin CX3C subunits cage shielding hydrophobic transmembrane segments preventing aggregation aqueous environment. For insertion they engage TIM22 translocase 300 kDa containing Tim22 twin voltage-gated pores each four helices Tim18 stabilizing Tim54 peripheral organizing Sdh3 subunit Complex II moonlighting Tim12 bridging small Tims. Membrane potential Delta psi drives hairpin-loop insertion positively charged loops electrophoresed lateral release bilayer. TIM23 pathway handles presequence matrix proteins via PAM motor, OXA inserts mitochondrially encoded hydrophobic subunits co-translationally matrix side, SAM assembles outer beta-barrels. TIM22 dedicated polytopic inner carriers essential metabolite exchange respiration regulation energy homeostasis and nucleotide transport across mitochondria.